The electroless plating is effected as a step for rendering a non-electrically conductive body such as synthetic resin products to become electrically conductive so that it may be subjected to the electrolytic plating, wherein the surface of the non-electrically conductive product to be plated is subjected to a pre-treatment for corroding it by any method to form very fine holes due to corrosion, and, in the electroless plating to be carried out subsequently, the plated layer is bonded to the surface of the base material by the anchoring effect of the metal to be deposited in the inner surface of the holes from the corrosion.
Further, there has been effected, for the printed circuit wiring board, a method, in which the electroless plating is carried out, after a curing type adhesive agent to be more corrosive than the base material is applied on the surface to be plated to corrode the surface.
This method accompanies, at any rate a corrosion step by use of strong chemicals, which corroding step comprises a pre-treatment step and post-treatment a step of defattening, rinsing, neutralizing, rinsing, etc. before and after this corroding step.
Further, as the conventional technique of intercepting the electromagnetic wave, there are various methods such as application of electrically conductive paint, flame coating of zinc, laminating layers of electrically conductive synthetic resin filled with an electrically conductive substance, or forming a sandwich structure with this electrically conductive synthetic resin layer as a core, and others. Of these various methods, the application of the electrically conductive paint has been widely used.
Any of these methods, however, cannot be said to have exhibited satisfactory effect. Even the most widely used electrically conductive paint is very expensive in price, and, in addition, the paint coating is required to be made thick, which would increase the cost for painting work.
In recent years, the electromagnetic wave intercepting effect of the coating formed by the electroless plating has become highly evaluated, but it has still not attained its diffusion owing to its point of problem to be mentioned hereinbelow.
Besides the conventional electroless plating technique comprises long and time-taking process steps, it is required to take anti-pollution measures, because the process utilizes a large quantity of strong corrosive liquid such as chromic acid, sulfuric acid, and so forth, as mentioned in the foregoing. Therefore, this technique has its restriction such that it cannot be put into practice where there is no facility for these measures, and also has an economical problem of bearing the cost for the anti-pollution measures.
When the plating is effected on a synthetic resin, special brands of resins adapted for the plating should be used, which resins are more expensive than ordinary resins. Therefore, no electroless plating is effected on the synthetic resins other than those which can meet the strict requirement for the interceptibility against electromagnetic wave.
In contrast to the conventional method for electroless plating of the synthetic resin, which makes use of the anchoring effect of a metal to be deposited in the inner surface of those corroded holes, the present inventors conceived a method, in which a solution of a hot-melt type adhesive agent is first applied to the surface to be plated, without corroding the same, and then the coating as applied is dried to thereby form a layer of the adhesive agent; after this, the electroless plating is effected on the layer of the adhesive agent; and, subsequently, the plated adhesive layer is heated to melt the adhesive layer, thereby causing the adhesive effect to appear. With this conception, they conducted various studies and experiments, and reached a conclusion that this plating method was feasible, when use is made of an adhesive agent containing therein a high molecular weight compound with the polar group being included in the composition, based on which finding they filed a previous patent application (vide: Japanese Patent Application No. 198207/1989 laid-open Mar. 19, 1991 as number 1-198207).
This method, however, is subjected to restrictions in the heating temperature, material to be plated, plating conditions, and so forth, for the reason that it comprises the final heating step, hence measures should be taken to prevent cracks from occurring due to difference in linear expansion coefficients between the material to be plated and the plated layer, during this heating step.
With a view to solving this problem, the present inventors have further conducted various studies on the compositions of the adhesive agents, in the course of which they discovered totally unexpected phenomenon such that copper is quickly deposited by the electroless plating on the coated film of a composition made up of a combination of styrene/butadiene/styrene block copolymer, not containing therein the polar group at all, and aliphatic/aromatic copolymer hydrocarbon type stickiness imparting resin, whereby a plated layer having favorable outer appearance is obtained, and, moreover, that this plated layer exhibited, according to the cross-cut adhesion test, its adhesive strength of 100/100, in its state as it is, without undergoing heating. From this unique phenomenon, they found out a clue for solving the abovementioned problem, and, as the result of various studies and experiments, they completed the present invention.